The majority of the proposed research is concerned with investigations of some of the reactions and key macromolecules of protein biosynthesis. A significant effort is directed at the underlying physical basis for the strong and specific association between aminoacyl tRNA synthetases and their cognate tRNA's, and between the elongation factor Tu and aminoacyl tRNA's. This kind of problem can be attacked by probing protein-nucleic acid complexes in such a way as to map the regions of tRNA which are and those which are not in contact with protein. In addition, cross-linked complexes may be studied. Structure-function relationships in aminoacyl tRNA synthetases and tRNA may be investigated by fluorescence methods, particularly using fluorescent probes covalently attached at specific sites.